1. Field of the Invention
This invention is directed to a method of supporting a roof, particularly a roof of an underground excavation such as a mine or tunnel, and to a system for carrying out the method, i.e., to apparatus for this purpose.
2. The Prior Art
In such underground excavations as mining galleries, tunnels and the like, the roof of the excavation must be supported against cave-in under the pressure of the overburden. Various approaches for effecting such support are known from the prior art. For example, in coal mining it is known to use the so-called "room and pillar system" in which roof bolting is used, i.e., steel rods or bars which penetrate the rock layers and hold them together to prevent collapse. It is also known to provide various kinds of supporting structures of wood and/or steel in which rigid or slightly yieldable supporting elements, for example pit props, are used to support the roof from below against collapse.
The problem with this latter type of approach, to which the present invention is also directed, is that the prior-art proposals are all relatively complicated and expensive and that the supports are difficult to erect and to move. The elements involved are relatively expensive and of considerable weight so that they are difficult to handle. There is also a pronounced lack of economy, both with respect to the materials involved and in the installation work required. As world petroleum resources begin to dwindle, increased emphasis is being placed on mining of coal; also, with the continuing decrease of such in-ground resources as minerals and the like there is a renewed interest in mining of deposits which in the past were abandoned because they were of poor quality and/or because they were too difficult to extract. In all these operations the question of cost effectiveness is, of course, of considerable importance in the determination whether they are economically feasible--and one of the factors which has a very substantial influence on these economic calculations is the cost of the roof supports which are required in large quantities. Further improvements in this field are, therefore, urgently needed.